PUBLIC STATEMENT: Traumatic brain injury (TBI) is a serious health problem suffered by 2% of the USA population with no pharmacological treatment available. This research will contribute to our understanding of how neurotrauma plays a role-in problems suffered by TBI patients by examining in mice the endoplasmic reticulum (ER) cell death pathway and how the protease caspase-12 contributes to cell death within the brain. The knowledge gleamed from this research may provide insights that could be useful in designing pharmacological treatments to alleviate the ongoing cellular loss suffered by TBI patients. The discovery that the protease caspase-12 is ER linked and activated by ER stress suggests a novel apoptotic pathway. WE HYPOTHESIZE THAT TBI INDUCES ER STRESS LEADING TO THE UNFOLDED PROTEIN RESPONSE (UPR). THIS INDUCES AND ACTIVATES PROCASPASE-12 BY CASPASE-7 AND/OR CALPAIN, WHICH CONTRIBUTES TO APOPTOTIC CELL DEATH. In the proposal's first 3 aims we will examine BiP (ER-molecular chaperone), caspase-7, caspase-12 and calpain in UPR and optimize the techniques and tools necessary to analyze their precise roles following TBI (Aims 4 &5). SPECIFIC AIM 1 will use primary cell cultures to study BiP induction and its relationship to the activation of caspase-7, caspase-12, and calpain, and to characterize antibodies designed to specifically recognize the calpain and caspase-7 mediated caspase-12 cleavage sites. SPECIFIC AIM 2 will examine the relative contribution of caspase-7 versus calpain in caspase-12 activation. In SPECIFIC AIM 3 the contribution of caspase-12 to the ER apoptotic pathway in siRNA treated primary cells will be assessed. SPECIFIC AIM 4 focuses on the relative contribution of caspase-7 versus calpain in caspase-12 activation following UPR induced by in vivo TBI using caspase-7 knockout mice. Finally, SPECIFIC AIM 5 focuses on the caspase-12 mediated ER apoptotic pathway's contribution to overall apoptotic cell death following TBI in caspase-12 knockout mice. The proposed research represents the first systematic examination of the ER apoptotic pathway after TBI. These studies will enhance our understanding of caspase-12-related cell death pathways, and provide important insights into TBI pathology that could ultimately provide therapeutic intervention and treatment of TBI related cell death, functional deficites, and linked Alzheimer's disease and epilepsy.